Disposable diapers and similar articles are commonly provided with closure systems. The closure comprises two opposing elements to be joined and fastener elements to effect this joining or closure. In conventional systems, the fastening elements are pressure-sensitive adhesive(PSA) fastening tabs permanently adhered to one element at one end(the manufacturers end) and preferably refastenably adhered to a second opposing element at a second end(the free end) of the fastening tab. With a disposable diaper, the two opposing elements or attachment surfaces are sides of the diaper and the PSA fastening tab is conventionally adhered at both ends to the same thin outer water-impermeable backsheet material, which conventionally is a thin polyethylene film (e.g., less than 1 mil thick). Therefore, the diaper PSA fastening tab has the conflicting goals of permanently and refastenably adhering to the same thin polyethylene film at opposing ends of the same tab. This is problematic as the same adhesive is used on both ends of the fastening tab, and a pressure-sensitive adhesive designed to permanently attach a tab to a thin diaper backsheet film will conventionally tear these thin films when the tab is removed, while adhesives designed to refastenably adhere a tab to a thin diaper backsheet film has a tendency to adhesively fail. A common solution proposed for this problem has been to strengthen the thin backsheet film with a reinforcement material in the diaper frontal region, at least where the free end of the tab is to be refastenably adhered, to prevent tearing. A common commercial approach has been to adhere a pressure-sensitive adhesive tape to the outside of the diaper backsheet film at this frontal region where the tab free end is refastenably attached. The tape backing acts as a reinforcing material, as well as serving as a predictable attachment surface for the free end of the PSA fastening tab. Alternatively, it has been proposed to place the reinforcement film on the interior surface of the backsheet in the frontal region and/or attach a reinforcement film by use of a hot-melt adhesive.
U.S. Pat. No. 4,643,730, proposes coating the interior of a diaper backsheet film in the frontal region with a radiation-curable coating such as urethane acrylate acrylic oligomers admixed with acrylate acrylic oligomers, epoxy acrylate acrylic oligomers or combinations thereof. However, the method described in this patent is expensive and requires a complicated and difficult-to-predict curable coating admixture.
U.S. Pat. No. 4,296,750 describes a diaper backsheet film reinforced with a hot-melt adhesive layer selectively applied to the portion of the backsheet refastenably adhered too by the free end of the fastening tab, i.e. the frontal region. Again, this solution is somewhat expensive and the temperature employed in applying the hot-melt adhesive layer generally has a tendency to distort or degrade thin polyethylene films. U.S. Pat. No. 4,210,144 similarly proposed applying hot-melt adhesive in the "mother's bond region" of the diaper backsheet where the adhesive fastening tab free end is releasably adhered(the frontal region). This patent describes applying adhesive glue beads or patterns of adhesive including continuous adhesive coatings. The adhesive beads are applied so that they span the width of the mother's bond region in the direction parallel with the direction of fastening tab attachment and removal. Again, this solution can adversely effect thin diaper backsheet films.
U.S. Pat. No. 3,867,940 proposes adhesively applying a scrim or a film to the mother's bond region, among other regions, of a diaper backsheet. The scrim or polymer film (e.g., biaxially orientated polyethylene terephthalate) can be applied to either the interior or exterior surface of the backsheet. The reinforcement described in this patent is the general commercial practice, however, the art continues to look for alternative methods.
U.S. Pat. No. 3,783,871 proposes reinforcing a diaper in the mother's bond region or refastening area by making the backsheet thicker in the areas where the fastening tab is adhered. The described method for selectively thickening the backsheet is a pulsed extruder. This method would be difficult to control and would require large amounts of resin to form the backsheet.
Despite the numerous proposed solutions outlined above, the art continues to search for new and unique ways for solving the problems of refastenability for a pressure-sensitive adhesive closure system, such as a diaper PSA fastening tab closure system using a reinforced frontal region as one attachment surface. The invention product and process provides a unique and highly advantageous structure and method for providing a reinforced region on a thin orientatable film without the use of costly separately applied reinforcement material(s), which reinforced region has a length and width suitable for use as a refastenable attachment surface of a diaper or like articles.